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## knapsack.md

      
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                CAIMEOX
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              October 11, 2025 13:59
            
              
                Scoped effects and data types a la carte
              
          
    knapsack 3 [1,2,3]


## braille.mbt
///|
fn braille_from_pos(pos : Array[(Int, Int)]) -> Char {
  let places = pos
    .map(fn {
      (1, 4) => 7
      (2, 4) => 8
      (1, n) => n
      (2, n) => n + 3
      _ => abort("invalid position")
    })

## effect.hs
{-# LANGUAGE QuantifiedConstraints #-}

import Data.Kind (Type)

type f ~> g = forall a. f a -> g a

class (forall f. (Functor f) => Functor (t f)) => HFunctor t where
  hmap :: (Functor f, Functor g) => (f ~> g) -> (t f ~> t g)

data FreeH (k :: (Type -> Type) -> (Type -> Type)) a where
	///\|
	fn braille_from_pos(pos : Array[(Int, Int)]) -> Char {
	let places = pos
	.map(fn {
	(1, 4) => 7
	(2, 4) => 8
	(1, n) => n
	(2, n) => n + 3
	_ => abort("invalid position")
	})
	{-# LANGUAGE QuantifiedConstraints #-}

	import Data.Kind (Type)

	type f ~> g = forall a. f a -> g a

	class (forall f. (Functor f) => Functor (t f)) => HFunctor t where
	hmap :: (Functor f, Functor g) => (f ~> g) -> (t f ~> t g)

	data FreeH (k :: (Type -> Type) -> (Type -> Type)) a where